1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to apparatuses and methods for providing an emergency service.
2. Description of the Related Art
Future communication systems are advancing to providing various high-speed high-capacity services to Mobile Stations (MSs). Examples of future communication systems include the Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system and the mobile Worldwide interoperability for Microwave Access (WiMAX) communication system. The mobile WiMAX communication system is based on the IEEE 802.16 communication system, and the IEEE 802.16 communication system corresponds to IEEE 802.16 standard.
An emergency service suggested in the IEEE 802.16 communication system is now described.
In general, the emergency service includes a Wireless Emergency Rescue Service (WERS) and a Wireless Emergency Alert Service (WEAS). The WER and WEA services will be explained individually. In a state of emergency such as a fire or a crime, the WERS locates the MS and supports a safe rescue. The WERS includes a voice call service such as a 911 service. Herein, since the WERS is mostly triggered by the MS, the WERS may be referred to as an MS-triggered emergency service. The WEAS includes a service which supports an emergency notification relating, for example, to weather such as a rainstorm, an impending earthquake, or a tidal wave, to the MS in a particular geographical region. Since the WEAS is triggered by a Base Station (BS) in general, the WEAS may be referred to as a BS-triggered emergency service.
The IEEE 802.16 communication system takes into account only the WEAS and suggests merely the operation of the BS for transmitting information relating to a transmission time of an emergency service message to the MS using a Broadcast Control Pointer Information Element (IE) message of a DownLink (DL)-MAP message. Herein, when the MS, in an idle mode or in a sleep mode, is out of service with the BS, the Broadcast Control Pointer IE message is used for the BS to broadcast transmission times of an Uplink Channel Descriptor (UCD) message, a Downlink Channel Descriptor (DCD) message, a MOBile Neighbor Advertisement (MOB_NBR-ADV) message, and the emergency service message to the MS in advance at a period predefined between the MS and the BS. Upon receiving the Broadcast Control Pointer IE message, the MS wakes up at the corresponding time point indicated by the Broadcast Control Pointer IE message or resumes the service with the BS and thus receives the corresponding UCD and DCD messages, the MOB_NBR-ADV message, and the emergency service message.
Operations of the idle MS in the IEEE 802.16 communication system are explained. The idle MS in the IEEE 802.16 communication system receives a MOBile PAGing ADVertisement (MOB_PAG-ADV) message from the BS in a paging listening interval of a preset paging cycle. Herein, the MOB_PAG-ADV message is transmitted from the BS to the idle MS to control the idle MS to carry out a network entry or a location updating. For example, when having DL data to be sent to the idle MS, for the DL data transmission, the BS may control the idle MS using the MOB_PAG-ADV message to wake up and enter the network or to update the location. Herein, the start point of the paging listening interval of the idle MS may differ according to the paging cycle and the paging offset of the idle MS.
As mentioned above, the emergency service message should be received at all of the sleeping MS, the normal MS, and the idle MS, and the message may be broadcast only once. To receive the emergency service message, the idle MS needs to wake up in the idle mode at the transmission time of the emergency service message from the BS and to wait to receive the emergency service message. However, when there is a plurality of idle MSs, the start points of the paging listening interval of the MSs may differ from each other. Accordingly, to inform the idle MSs which wake up at different time points of the transmission time of the emergency service message at a time, it is necessary to transmit the Broadcast Control Pointer IE messages as many times as the number of different start points of the paging listening intervals. However, since the Broadcast Control Pointer IE message includes a plurality of fields, the transmission of the Broadcast Control Pointer IE messages may cause a waste of resources.
In addition, at the emergency service message transmission time informed by the BS to the idle MS using the Broadcast Control Pointer IE message, the BS may fail to transmit the emergency service message. For instance, according to the scheduling of the BS, the emergency service message may be transmitted in a previous frame or a next frame, rather than the emergency service message transmission time indicated by the Broadcast Control Pointer IE message, that is, rather than the emergency service message transmit frame. In this situation, the idle MS, which wakes up according to the emergency service message transmission time indicated by the Broadcast Control Pointer IE message, may not receive the emergency service message in the corresponding frame. However, the IEEE 802.16e communication system does not provide any operating method when the idle MS may not receive the emergency service message at the emergency service message transmission time point indicated by the Broadcast Control Pointer IE message at all.
As discussed above, for the emergency service, the conventional IEEE 802.16 communication system merely defines the operation of broadcasting the information relating to the transmission time point of the emergency service message by use of the Broadcast Control Pointer IE message. In other words, the IEEE 802.16 communication system does not specify a method for providing the emergency service, except for the use of the Broadcast Control Pointer IE message. Thus, what is needed is an improved method for the emergency service in the IEEE 802.16 communication system.